Applications of laser produced continuum radiation

Abstract

High density high temperature plasmas produced m the foci of powerful pulsed laser beams have many applications and have been the subject of intensive investigations since high power lasers first became available. The work described in this thesis is iargly concerned with one particular application of laser generated plasmas that of photoabsorption spectroscopy of ionized species. The first chapter provides an introduction to the subject by reviewing the work done to date in this area and the various techniques which have been used to obtain absorption spectra. The usefulness of results obtained from VUV absorption spectra is also dealt with Recent work on the laser produced continuum source and the various applications which the source has found is also reviewed. A detailed description of the experimental method used to create two laser produced plasmas on separate targets and study the resulting absorptfon spectrum which is observed when continuum radiation emitted from one plasma is absorbed by the second plasma is given. New absorption spectra of magnesium aluminium and silicon plasmas are discussed and results are presented for the third fourth and fifth members of the neon-like isoeiectronic sequence Mg Hi Ai IV and Si V. The VUV absorption spectra of these ions have been recorded in the wavelength range 250 - 60A. This is the first recorded observation of absorption features along an extended isoeiectronic sequence. The wavelengths of the principal 2 s 22p 6 XS 0 - 2 s 2 2p sns nd transitions have been measured. Also the autoionizing levels due to inner 2s shell excitation 2s 22p6 1 S 0 - 2s 2p6np1 P 1 have been recorded and wavelengths for these features are given. Many new lines particularly in the spectra of aluminium and silicon plasmas are reported in this work for the first time. Extensive atomic structure calculations have been carried out In an attempt to assign these features. Calculations have also been carried out for the autoionizing levels of the neon-like sequence from Na II to Si V. The Xenon isoeiectronic sequence has also been studied m absorption and results are presented for the absorption spectrum of a lanthanum plasma. The 4d photoabsorption spectrum of La IV has been recorded for the first time in this work and this spectrum is discussed in terms of the previously observed 4d photoabsorption spectrum of Ba III. Progress on the evaluation of neutron scintillating glasses as new detector materials for the VUV spectral region is reported m Appendix 1 "I his application of laser produced conlinua is discussed and tentative results for cerium doped glass scintillators are presented. in Appendix 2 computer programs written over the course of this work are described. Examples of input and output data are given